Immediately before birth, the gastro-intestinal tract of a baby is thought to be sterile. During the normal process of birth, it encounters bacteria from the digestive tract, skin and environment of the mother and starts to become colonised. The faecal microbiota of healthy breast-fed infants which may be taken as the optimum microbiota for this age group is dominated by Bifidobacteria species with some Lactobacillus species and lesser amounts of Bacteroides such as Bacteriodes fragilis species, to the exclusion of potential pathogens such as Clostridia. After the completion of weaning at about 2 years of age, a pattern of gut microbiota that resembles the adult pattern becomes established.
It should be noted that, in the healthy breast-fed infant, Bifidobacteria form the basis of the microbiota accounting for 60-90% of total bacteria in the infant gut. Breast feeding also promotes intestinal barrier development which, together with bifidobacterial domination leads to enhanced absorption and therefore utilisation of ingested nutrition.
Mother's milk is recommended for all infants. However, in some cases breast feeding is inadequate or unsuccessful for medical reasons or the mother chooses not to breast feed. Infant formulae have been developed for these situations.
In the recent past, certain strains of bacteria have attracted considerable attention because they have been found to exhibit valuable properties for man if ingested. In particular, specific strains of the genera Lactobacilli and Bifidobacteria have been found to be able to colonise the intestinal mucosa, to reduce the capability of pathogenic bacteria to adhere to the intestinal epithelium, to have immunomodulatory effects and to assist in the maintenance of well-being. Such bacteria are sometimes called probiotics and it has already been proposed to add suitable probiotic bacteria to infant formulae.
Extensive studies have been carried out to identify new probiotic strains. For example, EP 0 199 535, EP 0 768 375, WO 97/00078, EP 0 577 903 and WO 00/53200 disclose specific strains of Lactobacilli and Bifidobacteria and their beneficial effects.
As indicated above, by reason of their abilities to colonise the intestinal mucosa and reduce the capacity of pathogenic bacteria to adhere to the intestinal epithelium, certain probiotic strains have already been proposed for the prevention and treatment of diarrhoea in infants. For example, WO 01/53201 proposes the use of Lactobacillus strains such as Lactobacillus paracasei CNCM I-2116 for the prevention or treatment of diarrhoea, specifically rotavirus-induced diarrhoea. A study is described in which the strain was administered to young children over a period of 29 days and it was found that the group of subjects receiving the strain had a 30% lower level of occurrence of episodes of diarrhoea during the study period.
However, incidence of episodes of infectious diarrhoea during the first few years remains a major concern for both parents and other care-givers and healthcare professionals.